Fix copying in a session nested in display-popup

tmux.conf

@@ -32,6 +32,9 @@ if '~/.config/tmux/check-version.sh "<" 3.2' \
   'set-option -as terminal-features ",xterm*:Tc"' \
   'set-option -as terminal-features ",xterm*:RGB"'
 
+# Declare clipboard (OSC-52) support so tmux emits it for copy-pipe.
+set -as terminal-features ',xterm*:clipboard'
+
 # Focus events enabled for terminals that support them
 set -g focus-events on
 
@@ -157,8 +160,10 @@ if -b '[ "$SSH_TTY" != "" ]' \
 if -b '[ "`uname`" = "Darwin" ]' \
   'bind -T copy-mode-vi y send-keys -X copy-pipe "pbcopy"'
 # When not in WSL2 use xsel, when in WSL use win32yank.exe to avoid UI lockups.
-if -b '[ "$WSLENV" = "" ]' \
+if -b '[ "`uname`" != "Darwin" ]' {
+  if -b '[ "$WSLENV" = "" ]' \
     'bind -T copy-mode-vi y send-keys -X copy-pipe "xsel -i --clipboard"' \
     'bind -T copy-mode-vi y send-keys -X copy-pipe "win32yank.exe -i -crlf"'
+}
 
 source-file ~/.config/tmux/theme.tmux